Oskar Schell is a nine-year-old boy grieving the loss of his Dad, Thomas Schell, who died in the terrorist attacks on the World Trade Center on September 11, 2001. Oskar is a very precocious boy: he’s extremely intelligent and curious, making up all sorts of esoteric inventions, but he also is scared and traumatized. Oskar feels incredibly guilty because his Dad left five phone messages on the morning of September 11, but he hasn’t told anyone about them; more importantly, he hasn’t told anyone that he was actually in the apartment for the final time that Dad called, but he was too afraid to pick up the phone. Oskar, who was never as close with his Mom as with his Dad, is growing even farther away from her. He has a loving and loyal relationship with his Grandma, but he’s still lonely and sad.
Oskar finds a key in his Dad’s closet; the key is in an envelope marked “Black.” Oskar decides to track down every person with the last name “Black” in New York City to try and figure out what the key unlocks. One of the people Oskar contacts happens to live in Oskar’s apartment building. Even though this Mr. Black hasn’t left his apartment for twenty-four years, he accompanies Oskar on his expedition.
Oskar’s expedition takes him to every corner of New York City. He must conquer many of his fears: he rides the subway, eats non-vegan food, crosses bridges, and entrusts himself to the mercy of strangers. When Oskar and Mr. Black travel to the top of the Empire State Building to meet Ruth Black, whose husband had been dead for many years, and who hasn’t left the top of the Empire State Building ever since. Mr. Black quits the expedition after that, which makes Oskar feel just as lonely and abandoned as when he’d begun.
The novel also has a parallel storyline about Oskar’s grandparents. Grandpa, who is also named Thomas Schell, was in Dresden, Germany, during World War II, when the city was firebombed. Practically all the people most important to Grandpa––Grandpa’s lover, Anna, his unborn son, and his parents––were killed in the explosion. The trauma and aftermath caused Grandpa to lose his ability to speak. He has “YES” and “NO” tattooed on his hands, and he carries around a daybook, on which he writes notes to communicate. Several of the chapters are in the form of letters written by Grandpa to his “unborn son”: this “son” could either be Oskar’s Dad or the child that Anna, his lover, was pregnant with when she died in Dresden.
After the firebombing of Dresden, Grandpa moves to New York, where he meets Grandma. He recognizes her from Germany: Grandma is Anna’s sister. Grandpa can’t speak at this point, but they communicate through gestures and the daybook. Grandma poses nude for Grandpa, who is a sculptor, but the sculpture just ends up looking like Anna. Despite the fact that Grandpa’s still in love with Anna, he and Grandma marry. They designate certain areas of the apartment as “Nothing” and “Something” and concoct elaborate rules that limit their contact with each other. Nevertheless, Grandma gets pregnant, breaking their rules. Before Dad is born, Grandpa leaves Grandma and flies back to Dresden.
On September 11, Grandpa sees the bombing on television, and he reads Dad’s name in the obituaries. Grandpa immediately gets on a plane to Manhattan, even though he hasn’t been to the United States in forty years. He phones Grandma, even though he can’t talk, then leaves her notes; eventually, she lets him move back into the apartment, though only into the guest room.
In addition to the letters from Grandpa, Jonathan Safran Foer includes a long letter from Grandma to Oskar, spread across several chapters. Grandma is writing to Oskar about her past. Throughout the novel, it’s not quite clear why Grandma is sending Oskar such a long letter, since she lives in the next building over, and they see each other every day. But at the end of the novel, the letter finally reveals that Grandma and Grandpa are now living in the airport: she has convinced him to stay with her in this limbo land instead of flying away following the events of Oskar’s quest.
The two stories—the expedition and the grandparents’ history––converge when Oskar meets “the renter”—that is, Grandpa—and Oskar tells him the entire story about Dad and the search for the lock that the key opens. Oskar also checks the phone messages for the first time in eight months and discovers a message from Abby Black, the second Black he’d visited. She says that her husband, William, knows what the key is for. The message cuts off halfway. When Oskar visits Abby, he learns why the message cuts off in the middle—that’s when Mom picked up the phone, and Abby told her everything. Mom has been monitoring the expedition the entire time, it appears. (So has Grandpa, actually.) Oskar goes to William’s office and gives him the key, which William says is for his dad’s safety deposit box. William offers to let Oskar come with him when he opens the box, but Oskar refuses.
On the second anniversary of Dad’s death, Oskar and Grandpa go to the cemetery to dig up Dad’s empty coffin. Grandpa buries the unsent letters addressed to his son into the grave.
Jonathan Safran Foer’s style of storytelling is visual as well as narrative. When characters take photographs or describe images, these often appear in the body of the chapter. In the letters from Grandpa often appear excerpts from Grandpa’s daybook. The novel ends with Oskar’s flipbook of a man falling from the building, but in reverse order, so the man appears to be falling up.